Leach aid for metal recovery

ABSTRACT

Methods of recovering metals from metal-bearing materials, and more particularly, methods for improving leaching efficiency in extraction processes by employing a surfactant composition in the extraction process, as well as slurries useful in the methods of recovering metals are provided.

TECHNICAL FIELD

The present disclosure relates to compositions and processes forrecovering metal values from metal-bearing materials, e.g., ores,concentrates, and other metal-bearing materials.

BACKGROUND

One approach to separating metals from metal-bearing materials includessubjecting the ground or crushed material to treatment with a chemicalsolution containing one or more reagents capable of selectivelysolubilizing the desired metal constituents while leaving the remainderof the metal-bearing material behind. The leach solution may then betreated in further recovery and refining operations to obtain the metalvalues in a purified form. Despite available technologies, there is aneed in the art for improved methods of recovering metal values frommetal-bearing materials.

SUMMARY

A method of extracting metal from a metal-bearing material is provided.The method comprises forming a slurry comprising the metal-bearingmaterial, water, a surfactant composition, and a leaching composition.At least a portion of the metal from the slurry is recovered.

A method of improving leaching efficiency in a metal extraction processis provided. The method comprises treating a metal-bearing material witha surfactant composition. The treated metal-bearing material issubjected to a metal extraction process.

A slurry is provided. The slurry comprises water; a metal-bearingmaterial comprising at least one of gold, silver, and copper; a highterpene-containing natural oil; and a leaching agent comprising at leastone of an acid and a cyanide.

The metal-bearing material may be comminuted prior to formation of theslurry. The metal-bearing material may be treated with the surfactantcomposition prior to, during, or after comminution. The comminutedmetal-bearing material may be formulated as an aqueous slurry includingthe comminuted metal-bearing material.

The surfactant composition may include an anionic surfactant selectedfrom the group consisting of an alkyl aryl sulfonate, an olefinsulfonate, a paraffin sulfonate, an alcohol sulfate, an alcohol ethersulfate, an alkyl carboxylate, an alkyl ether carboxylate, anethoxylated alkyl phosphate ester, a monoalkyl sulfosuccinate, a dialkylsulfosuccinate, a monoalkyl sulfosuccinamate, a dialkylsulfosuccinamate, and combinations thereof.

The surfactant composition may include a cationic surfactant selectedfrom the group consisting of an alkyl trimethyl quaternary ammoniumsalt, an alkyl dimethyl benzyl quaternary ammonium salt, a dialkyldimethyl quaternary ammonium salt, an imidazolinium salt, andcombinations thereof.

The surfactant composition may include a nonionic surfactant selectedfrom the group consisting of an alcohol alkoxylate, an alkylphenolalkoxylate, a block copolymer of ethylene oxide, a block copolymer ofpropylene oxide, and a block copolymer of butylene oxide, an alkyldimethyl amine oxide, an alkyl-bis(2-hydroxyethyl) amine oxide, an alkylamidopropyl dimethyl amine oxide, analkylamidopropyl-bis(2-hydroxyethyl) amine oxide, an alkylpolyglucoside, a polyalkoxylated glyceride, a sorbitan ester, apolyalkoxylated sorbitan ester, an alkoyl polyethylene glycol ester, analkoyl polyethylene glycol diester, multiples thereof, and combinationsthereof.

The surfactant composition may include a high terpene-containing naturaloil.

The surfactant composition may be present in the slurry at aconcentration of from about 1 gram of surfactant composition to about10,000 grams of surfactant composition per metric ton of metal-bearingmaterial. The surfactant composition may be present in the slurry at aconcentration of from about 10 grams of surfactant composition to about100 grams of surfactant composition per metric ton of metal-bearingmaterial.

The leaching composition may include a leaching agent selected from thegroup consisting of nitric acid, hydrofluoric acid, hydrochloric acid,sulfuric acid, phosphoric acid, perchloric acid, a carbonate, ahydroxide base, gaseous ammonia, a cyanide salt, ferric sulfate, ferricchloride, cupric chloride, ferrous chloride, ozone, a thiosulfate salt,thiourea, thiosulfuric acid, dithiooxamide, a substituted dithiooxamide,a halogen-containing compound, and combinations thereof. The leachingagent may be at least one of sodium cyanide, potassium cyanide, andcalcium cyanide.

The recovered metal may be gold, silver, platinum, palladium, titanium,or nickel.

The metal-bearing material may be ore.

The metal-bearing material may be treated with the leaching compositionin a stirred reactor.

In another aspect, disclosed is a method of improving leachingefficiency in a metal extraction process, the method including treatinga metal-bearing material with a surfactant composition; and subjectingthe treated metal-bearing material to a metal extraction process. Themetal-bearing material may be comminuted before or during treatment withthe surfactant composition. The extraction process may include at leastone of in-situ leaching, dump leaching, heap leaching, vat leaching,agitated leaching, and combinations thereof.

The compositions, methods, and processes are further described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram depicting an exemplary process of leachingmetal from a metal-bearing material.

FIG. 2 is a flow diagram depicting an exemplary process of recoveringmetal from a metal-bearing material.

FIG. 3 is a flow diagram depicting an exemplary process of recoveringgold from a gold-bearing material.

DETAILED DESCRIPTION

Disclosed are methods of improving extraction of metal from ametal-bearing material. The methods include treating a metal-bearingmaterial with a surfactant composition, and leaching a metal from thetreated metal-bearing material. The metal-bearing material may betreated with the surfactant composition at any suitable point in theextraction process. In certain embodiments, the surfactant compositionimproves leaching of metal from metal-bearing material. While notwishing to be bound by theory, it is believed that the surfactantcomposition reduces surface tension of leaching agent solutions atparticle surfaces of the metal-bearing material. The reduced surfacetension is believed to allow for increased exposure of metal-bearingparticle surfaces to the leaching agents added during the extractionprocess, which in turn is believed to allow for greater dissolutionand/or chemical reaction of the metal with the leaching agent(s).

The methods provide several advantages over current technologies. Inparticular, the methods can improve leaching efficiency and metalrecovery from metal-bearing materials. The methods can be implementedinto current extraction processes with minimal capital investment, usingequipment already in place.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art. In case of conflict, the present document, includingdefinitions, will control. Preferred methods and materials are describedbelow, although methods and materials similar or equivalent to thosedescribed herein can be used in practice or testing of the presentinvention. All publications, patent applications, patents and otherreferences mentioned herein are incorporated by reference in theirentirety. The materials, methods, and examples disclosed herein areillustrative only and not intended to be limiting.

As used in the specification and the appended claims, the singular forms“a,” “an” and “the” include plural references unless the context clearlydictates otherwise. The terms “comprise(s),” “include(s),” “having,”“has,” “can,” “contain(s),” and variants thereof, as used herein, areintended to be open-ended transitional phrases, terms, or words that donot preclude the possibility of additional acts or structures. Thepresent disclosure also contemplates other embodiments “comprising,”“consisting of” and “consisting essentially of,” the embodiments orelements presented herein, whether explicitly set forth or not.

As used herein, the term “agglomeration” refers to a process where smallparticles, such as fines, combine into larger masses or clumps, orcombine together with larger particles.

As used herein, the term “flotation” refers to a process forconcentrating minerals from their ores. In a flotation process, the oremay be crushed and wet ground to obtain a pulp. Additives such asflotation or collecting agents and frothing agents may be added to thepulp to assist in subsequent flotation steps in separating valuableminerals from the undesired, or gangue, portion of the ore. Theflotation or collecting agents can comprise liquids such as oil, otherorganic compounds, or aqueous solutions. Flotation may be accomplishedby aerating the pulp to produce froth at the surface. Minerals, whichadhere to the bubbles or froth, can be skimmed or otherwise removed andthe mineral-bearing froth collected and further processed to obtain thedesired minerals.

As used herein, the term “pregnant solution” refers to a solutioncarrying a dissolved metal, mineral, and/or a desired solute. A pregnantsolution may carry residual leaching agents, and/or other materials. Thepregnant solution may carry soluble ions or metallic complexes. Thepregnant solution may be unsaturated in a desired solute, or may beliquor saturated in desired solute.

As used herein, the term “barren solution” refers to leaching solutionthat has been previously used within a leach process (e.g., was once apregnant leach solution) and has been processed or otherwisesufficiently reconstituted (e.g., recycled).

As used herein, the term “metal value” may refer to a metal component orcomponents targeted for recovery from a metal-bearing material (e.g., amineral ore).

Disclosed are methods of improving leaching efficiency frommetal-bearing material in extractive metallurgy processes. The methodsinclude treating the metal-bearing material (e.g., an ore material) witha surfactant composition. The metal-bearing material may be treated withthe surfactant composition at any suitable point in an extractionprocess, preferably before and/or during treatment with a leachingcomposition. The surfactant composition can be added to a rawmetal-bearing material (e.g., raw ore material), a crushed metal-bearingmaterial, a ground/milled metal-bearing material, and/or a slurry ofmetal-bearing material. The surfactant composition can be applied to ametal-bearing material during pre-leaching processes (e.g., duringtransport, during crushing, grinding, mixing, or during blending into aslurry). The surfactant composition can be combined with one or morecompositions, before or during application to a metal-bearing material.The surfactant composition can be combined with a leaching compositionand applied concurrently to a metal-bearing material.

In certain embodiments, the methods include treating a raw ore materialwith a surfactant composition, comminuting the treated ore material(e.g., wet or dry crushing and/or wet or dry grinding), and leaching oneor more selected metals from the comminuted, treated ore material. Incertain embodiments, the methods include treating a comminuted orematerial with a surfactant composition, and leaching one or moreselected metals from the comminuted, treated ore material. In certainembodiments, the methods include treating a slurry of comminuted orematerial with a surfactant composition, and leaching one or moreselected metals from the treated slurry of ore material. In certainembodiments, the methods include treating a comminuted ore material witha composition including a surfactant composition and a leachingcomposition, and leaching one or more selected metals from thecomminuted, treated ore material.

An exemplary process of the present disclosure may include: comminutinga metal-bearing material; treating the comminuted material with aneffective amount of a surfactant composition; and adding an effectiveamount of a leaching composition to the treated, comminuted material.The process may include mixing the comminuted material (before, during,and/or after treatment with the surfactant composition) with water toproduce a slurry. The process may include adding an effective amount ofa leaching composition to the slurry (before, during, and/or aftertreatment with the surfactant composition.)

FIG. 1 is a flow chart depicting an exemplary extraction process andoptional points of addition of surfactant composition in the exemplaryprocess. As shown, a surfactant composition may be delivered to a rawore material (addition point A). The treated raw ore material may besubjected to a leaching process thereafter, such as dump leaching, heapleaching, vat leaching, or agitated leaching, as discussed below. Asurfactant composition may be delivered to an ore material prior to,during, and/or immediately after a crushing phase (addition point B).The treated, crushed ore material may be subjected to a leaching processthereafter, such as heap leaching, vat leaching, or agitated leaching. Asurfactant composition may be delivered to an ore material prior to,during, and/or immediately after a grinding phase (addition point C).The treated, ground ore material may be subjected to a leaching processthereafter, such as vat leaching or agitated leaching. A surfactantcomposition may be delivered to an ore material after a flotation phase(addition point D). The treated ore material may be subjected to aleaching process thereafter, such as vat leaching or agitated leaching.A surfactant composition may be delivered to an ore material after athermal pre-treatment phase (addition point E). The treated ore materialmay be subjected to a leaching process thereafter, such as vat leachingor agitated leaching. A surfactant composition may be delivered to anore material prior to and/or during an in-situ leaching process(addition point F). A surfactant composition may be delivered to an orematerial prior to and/or during a dump leaching process (addition pointG).

FIG. 2 is a flow chart depicting another exemplary process implementingthe disclosed methods. An ore material 1 can be conveyed to a grinder 2(e.g., a ball mill) and crushed and/or ground (e.g., wet or dry crushingand/or wet or dry grinding). The ore material may be crushed and/orground to any selected particle size (e.g., 100%—65 Tyler mesh, or100%—100 Tyler mesh). The crushed and/or ground ore material may betreated with a solution (e.g., an aqueous solution) to produce an oreslurry during and/or after the comminution process. The slurry may haveany selected solids content (e.g., between 35% and 55%, or between 40%and 50% by weight). The comminuted ore material may be conveyed to afixed bed 3 (e.g., an impermeable plastic and/or clay lined leach pad).The ore on the fixed bed 3 may be treated with a leaching composition 4(e.g., an aqueous solution of cyanides, thiourea, or thiosulfuric acid).The leaching composition may percolate through the ore material andextract one or more selected minerals (e.g., gold, silver, platinum,indium, gallium, lead, zinc, copper, nickel, uranium) from the ore toprovide a pregnant solution 5. The pregnant solution 5 may be processedto remove waste materials 7 and thereafter concentrated and refined 6for purification of the metal(s). Waste 7 may be processed asappropriate.

As shown in FIG. 2, a surfactant composition may be delivered to the rawore material at one or more points in the extraction process. Thesurfactant composition may be delivered to a raw ore material beforecomminution (addition point A); the surfactant composition may bedelivered to the ore material during comminution (addition point B); thesurfactant composition may be delivered to the ore material aftercomminution (addition point C) and before delivery to the fixed bed 3;the surfactant composition may be delivered to the ore material on thefixed bed 3 (addition point D), and throughout the leaching process asdesired; and/or the surfactant composition may be mixed with theleaching composition (addition point E) and delivered simultaneously tothe ore material along with the leaching composition. The surfactantcomposition may be delivered, for example, via mechanical conveyance,dilute or dense phase conveyance, or pneumatic conveyance. Thesurfactant composition may be provided in a controlled manner using avolumetric or gravimetric feeder, for example.

FIG. 3 is a flow chart depicting another exemplary process implementingthe disclosed methods, wherein the process includes a cyanide leachingsystem used for gold extraction. A metal-bearing material may be treatedwith a leaching composition. Activated carbon may then be used to adsorbdesired metals from the pregnant leach solution, and free leach agentmay be sent back to the leaching process through a barren pond. Boundmetals may be stripped from the carbon, and the carbon may bereactivated in a kiln for further use. The stripped metals may beisolated from solution by electrowinning and smelting.

The disclosed methods may provide metal recovery rates of about 80% to100%, about 85% to 100%, about 90% to 100%, or about 95% to 100%recovery from metal-bearing materials. The disclosed methods may providemetal recovery rates of about 80% or greater, about 81% or greater,about 82% or greater, about 83% or greater, about 84% or greater, about85% or greater, about 86% or greater, about 87% or greater, about 88% orgreater, about 89% or greater, about 90% or greater, about 91% orgreater, about 92% or greater, about 93% or greater, about 94% orgreater, about 95% or greater, about 96% or greater, about 97% orgreater, about 98% or greater, about 99% or greater, or 100%.

The disclosed methods may provide an improvement in leaching efficiencywhen compared to a control (0 ppm of surfactant composition), of about0.5% to about 1%, about 0.5% to about 1.5%, about 0.5% to about 2%,about 0.5% to about 5%, about 0.6% to about 1%, about 0.7% to about 1%,about 0.8% to about 1%, about 0.9% to about 1%, or about 1%. Thedisclosed methods may provide an improvement in leaching efficiency whencompared to a control (0 ppm of surfactant composition), of about 0.5%or greater, about 0.6% or greater, about 0.7% or greater, about 0.8% orgreater, about 0.9% or greater, or about 1% or greater.

The disclosed methods employ at least one surfactant composition. Thesurfactant composition includes one or more compounds that improveleaching efficiency in extraction processes. While not wishing to bebound by theory, the surfactant composition is believed to improveleaching from metal-bearing materials (e.g., mineral ores) by reducingsurface tension of the leaching solution at particle surfaces. Thereduced surface tension is believed to increase wetting of particlesurfaces with the leaching composition, leading to improved extractionof metal.

Surfactant compounds suitable for inclusion in the surfactantcompositions include, but are not limited to, anionic surfactants,cationic surfactants, zwitterionic surfactants, nonionic surfactants,and combinations thereof. Anionic surfactants include alkyl arylsulfonates, sulfonates, paraffin sulfonates, alcohol sulfates, alcoholether sulfates, alkyl carboxylates and alkyl ether carboxylates, alkyland ethoxylated alkyl phosphate esters, and mono and dialkylsulfosuccinates and sulfosuccinamates. Cationic surfactants include, butare not limited to, alkyl trimethyl quaternary ammonium salts, alkyldimethyl benzyl quaternary ammonium salts, dialkyl dimethyl quaternaryammonium salts, and imidazolinium salts. Nonionic surfactants include,but are not limited to, alcohol alkoxylates, alkylphenol alkoxylates,block copolymers of ethylene, propylene and butylene oxides, alkyldimethyl amine oxides, alkyl-bis(2-hydroxyethyl) amine oxides, alkylamidopropyl dimethyl amine oxides, alkylamidopropyl-bis(2-hydroxyethyl)amine oxides, alkyl polyglucosides, polyalkoxylated glycerides, sorbitanesters and polyalkoxylated sorbitan esters, and alkoyl polyethyleneglycol esters and diesters. Also included are betaines and sultanes,amphoteric surfactants such as alkyl amphoacetates and amphodiacetates,alkyl amphopropionates and amphodipropionates, andalkyliminodiproprionate. A preferred surfactant compound suitable forinclusion in the surfactant composition comprises at least one of C₁₄₋₁₆alpha olefin sulfonate and sodium dodecyl benzene sulfonate.

In certain embodiments of the inventive methods, the surfactantcompositions include at least one of a quaternary ammonium compound, anamine oxide, an ionic or non-ionic surfactant, and combinations thereof.Suitable quaternary ammonium compounds include, but are not limited to,alkyl benzyl ammonium salt; benzyl cocoalkyl(C₁₂-C₁₈)dimethylammoniumsalt; dicocoalkyl (C₁₂-C₁₈)dimethylammonium salt; ditallowdimethylammonium salt; di(hydrogenated tallow alkyl)dimethyl quaternaryammonium methyl salt; methyl bis(2-hydroxyethyl cocoalkyl(C₁₂-C₁₈)quaternary ammonium salt; dimethyl(2-ethyl) tallow ammonium methyl salt;n-dodecylbenzyldimethylammonium salt; n-octadecylbenzyldimethyl ammoniumsalt; n-dodecyltrimethylammonium salt; soya alkyltrimethylammonium salt;and hydrogenated tallow alkyl (2-ethylhyexyl) dimethyl quaternaryammonium methyl salt. Preferred salts of the aforementioned compoundsare chlorides and/or sulfates.

Water soluble non-ionic monomers include, but are not limited to,acrylamide, N-substituted derivatives of acrylamide, hydroxyalkylacrylates, and hydroxyalkyl methacrylates. Anionic monomers include, butare not limited to, salts of acrylic acid, methacrylic acid, ethacrylicacid, α-chloroacrylic acid, crotonic acid, itaconic acid, maleic acid,fumaric acid, vinyl sulfonic acid, and 2-acrylamido-2-methyl propanesulfonic acid. Cationic monomers include, but are not limited to,quaternary salts of dialkyl amino ethyl methacrylate, diallyl dimethylammonium chloride, vinyl benzyl-trimethyl ammonium chloride and thelike. In certain embodiments, the nonionic monomers in the swellablepolymer are selected from the group consisting of: acrylamide,N—N-dimethylacrylamide, 2-hydroxyethyl methacrylate, and combinationsthereof.

In certain embodiments, the anionic monomers in the swellable polymer isan alkali (e.g., sodium) salt of a compound selected from the groupconsisting of: acrylic acid, methacrylic acid, 2-acrylamido-2-methylpropane sulfonic acid, and combinations thereof. In certain embodiments,the cationic monomer in the swellable polymer is diallyl dimethylammonium chloride. The water swellable cross-linked polymer can besynthesized with compounds having two ethylenic groups copolymerizablewith water soluble monomers. Exemplary cross-linkers includeN—N′-methylene-bis-acrylamide, N,N′-methylene-bis-methacrylamide, analkylidene-bis-acrylamide, divinyl benzene sulfonate, ethylene glycoldiacrylate, ethylene glycol dimethacrylate, diallyl ethylene glycolether, divinyl ester of polyethylene glycol (e.g., polyethyleneglycol-600 diacrylate), divinyl ether of polyethylene glycol and thelike difunctional monomers.

In certain embodiments, the surfactant composition includes a nonionicsurfactant. In certain embodiments, the nonionic surfactant is acoco-n-alcohol amine or amide, which in certain embodiments iscocodiethanolamide.

In certain embodiments, at least one of the water soluble brancher andthe cross-linking agent is an adduct of glycerine and allyl glycidylether referred to herein as “B-brancher.” Other types of branchersinclude the adducts of allylamine and a copolymer of maleic anhydrideand methyl vinyl ether having differing mole ratios of allylamine toanhydrides, referred to herein as “A-branchers.”

In certain embodiments, the surfactant compositions includes ahomopolymer or copolymer of diallyldimethyl ammonium chloride(“DADMAC”), such as described in U.S. Pat. No. 4,561,905, which isincorporated herein by reference in its entirety. The copolymers maycontain from about 5 mole percent to about 30 mole percent of a watersoluble anionic monomer. These copolymers may be referred to aspolyampholytes. In a preferred embodiment, the anionic monomer is atleast one of acrylic acid and methacrylic acid, which is sometimesdenoted as (meth)acrylic acid. The polymers may have an IntrinsicViscosity of at least 0.3, as measured in 1 M NaNO₃ at 30° C. The amountof water soluble anionic monomer polymerized with DADMAC may vary fromas little as about 5 mole percent to as much as about 30 mole percent.While methacrylic and most preferably acrylic acid are preferredmonomers for copolymerization with DADMAC, other anionic vinyl monomersmay be employed. Examples of such monomers are maleic acid, itaconicacid and fumaric acid. Furthermore, diluent monomers may beter-polymerized with the DADMAC and the water soluble anionic monomer,and may be used in amounts of up to about 10 mole percent. Preferreddiluent monomers are the hydroxy C₂-C₆ alkyl acrylates and/ormethacrylates. Other diluent monomers that may be utilized include, butare not limited to, acrylonitrile, acrylamide, styrene, vinyl acetate,and the like. The polymer containing the diluent monomers are attractivefrom the standpoint that most of the diluent monomers are inexpensiveand in most cases do not materially detract from the activity of theDADMAC copolymer into which they have been incorporated. The co- andterpolymers of DADMAC as generally described above are illustrated ingreat detail in U.S. Pat. No. 4,715,962, the disclosure of which isincorporated herein by reference in its entirety. The polymer may be inthe form of an aqueous solution or in the form of a water-in-oilemulsion, which in the presence of certain water soluble surfactant(s)invert into water and allow the polymer contained in the emulsion todissolve rapidly. The dosage of the DADMAC polymer may be at least about25 parts per million of polymer (i.e., grams of polymer per metric tonof metal-bearing material treated), preferably from about 50 parts permillion to about 2,000 parts per million. The DADMAC polymer, includingcopolymer and terpolymer, may be in the form of an aqueous solutionwherein the polymer content in the aqueous solution is from about 10percent to about 50 percent by weight of the aqueous solution.

In certain embodiments, the surfactant composition includes a surfactantcompound and a high terpene-containing natural oil, such as described inU.S. Pat. Nos. 5,330,671; 5,527,482; 5,863,456; 5,876,622; 5,958,287;and 6,124,366, each of which is incorporated herein by reference in itsentirety. Surfactant compositions including a surfactant compound and ahigh terpene-containing natural oil are marketed as part of DUSTFOAMsuppression systems by Enviroflo Engineering, an Ecolab Company. Highterpene-containing natural oils are those natural oils having a terpenecontent of at least about 50%. The high terpene-containing natural oilmay contain at least about 90% terpene. Suitable high terpene-containingnatural oils include, but are not limited to, citrus peel oil, whichincludes, but is not limited to, orange peel oil (i.e., orange oil),grapefruit peel oil (i.e., grapefruit oil), and lemon peel oil (i.e.,lemon oil). Orange peel oil is preferred in certain embodiments, as itcontains from about 90% to about 94% terpene and is very abundant incertain parts of the world. Pine oil is also a useful highterpene-containing natural oil.

The surfactant composition may include from about 1% to about 15% byweight high terpene-containing natural oil, preferably from about 8 toabout 12% by weight, and more preferably from about 8 to about 10% byweight. The amount of high terpene-containing natural oil will dependupon the amount of terpene in the high terpene-containing natural oil.For example, in the case of orange peel oil, the orange peel oil can bepresent in the surfactant composition in an amount of from about 1 toabout 15% by weight, or from about 8% to about 10% by weight. Theterpene may break up oily (fatty) deposits on ore particles allowing theleaching agent(s) to better contact the ore particles. Conventionalsurfactants can be used in combination with the high terpene-containingnatural oil, such as at least one of an anionic surfactant and anonionic surfactant. Preferred is an anionic surfactant such as a saltof a fatty acid, an alkyl sulfate, an alkyl ether sulfonate, an alkylaryl sulfonate, multiples thereof, and combinations thereof. Examples ofpreferred surfactants include sodium dodecylbenzene sulfonate, sodiumlauryl ether sulfate and salts such as a sodium salt of a secondaryalkane sulfonate (e.g., Hostaspun SAS 60 marketed by Hoechst).Furthermore, the use of ethoxylated nonylphenols with, e.g., from about8 to about 10 moles of ethylene oxide and/or ethoxylated octylphenolswith, e.g., from about 8 to about 10 moles of ethylene oxide (e.g.,alkylaryl polyglycol ether N9), may be utilized as well. In certainembodiments, the surfactant composition contains up to about 40% byweight surfactant(s), preferably from about 15% to about 25% by weightsurfactant(s), and more preferably from about 20% to about 22% byweight.

The surfactant composition may further comprise a variety of additivessuch as, for example, an antioxidant and/or a preservative. An exampleof a suitable antioxidant is butylated hydroxytoluene (i.e.,2,6-di-tert-butyl-para-cresol; “BHT”). The antioxidant may be present inthe composition in an amount of from about 0.01% to about 1% by weight,preferably from about 0.08% to about 0.12% by weight. Suitablepreservatives include, but are not limited to, formaldehyde,methylparaben, propylparaben, borax, and combinations thereof. Thepreservative may be present in the composition in an amount of fromabout 0.5% to about 5% by weight, preferably from about 0.8% to about1.2% by weight.

When in an aqueous composition, water may make up the majority of thesurfactant composition. Generally, when in an aqueous composition, thesurfactant composition may comprise from about 60% to about 80% byweight water, including from about 60%, or from about 63%, or from about66%, to about 80%, or to about 75%, or to about 70% by weight water. Thewater may be derived from fresh water, sea water, brine, mixtures ofwater and non-toxic water soluble organic compounds, recycled processwater, and combinations thereof.

An example of an effective surfactant composition comprises about 11%sodium dodecyl benzene sulfonate, about 5% sodium lauryl ether sulfate,about 9% cold pressed orange peel oil, about 3% alkyl arylpolyglycolether N9, about 1% of a sodium salt of a secondary alkanesulfonate, about 1% formaldehyde, and about 0.1% of an antioxidant; withthe balance being water (all percentages are by weight). A furtherexample of an effective surfactant composition comprises 10.95% (i.e.,about 11%) sodium dodecyl benzene sulfonate, 5.1% (i.e., about 5%)sodium lauryl ether sulfate, 9.1% (i.e., about 9%) cold pressed orangeoil, 3.5% (i.e., about 3%) alkyl aryl polyglycolether N9, 1.4% (i.e.,about 1%) of a sodium salt of a secondary alkane sulfonate, 1%formaldehyde, and 0.1% of an antioxidant. In certain embodiments, thebalance is water (all percentages are by weight).

Another example of an effective surfactant composition comprises fromabout 15% to about 20% (e.g., about 17%) C₁₄₋₁₆ alpha olefin sulfonate,from about 0.1% to about 3% (e.g., about 1%) orange peel oil, from about0.1% to about 2% (e.g., about 0.6%) cocodiethanolamide, and from about0.01% to about 1% (e.g., about 0.1%) antioxidant. In certainembodiments, the balance is water (all percentages are by weight).

The surfactant composition may be dosed to the metal-bearing material inan amount of from about 1 part per million (ppm) to about 10,000 ppm,including from about 1 ppm, or from about 5 ppm, or from about 10 ppm,or from about 15 ppm, or from about 20 ppm, to about 10,000 ppm, or toabout 1,000 ppm, or to about 500 ppm, or to about 100 ppm, or to about50 ppm, or to about 40 ppm. In a preferred embodiment, the surfactantcomposition is dosed to the metal-bearing material in an amount of fromabout 20 ppm to about 40 ppm. Referring to the dosage of the surfactantcomposition, the term “part(s) per million” (i.e., “ppm”) refers tograms of surfactant per metric ton of metal-bearing material (e.g., ore)treated. The surfactant composition may be dosed to the metal-bearingmaterial in an amount of about 1 ppm or greater, or about 5 ppm orgreater, or about 10 ppm or greater, or about 15 ppm or greater, orabout 20 ppm or greater, or about 25 ppm or greater, or about 30 ppm orgreater, or about 35 ppm or greater, or about 40 ppm or greater, orabout 45 ppm or greater, or about 50 ppm or greater. Dosages are basedupon total surfactant composition in the metal-bearing material.

The disclosed methods may be used with any type of leaching compositionsuitable for extraction processes. The leaching composition is combinedat some point during the surfactant exposure to extract metal from themetal-bearing material, wherein leaching efficiency may be enhanced dueto less surface tension created by activity of the surfactantcomposition. Leaching compositions include at least one leaching agent,e.g., an acid, a base, or a salt. It is to be understood that one ormore leaching agents may be used in combination. The leachingcomposition may further include an additive, which may be a solvent.

In certain embodiments, the leaching agent is an acid, which may be aweak acid, a strong acid, or a combination of several acids. Suitableacids include, but are not limited to, nitric acid, hydrofluoric acid,hydrochloric acid, sulfuric acid, phosphoric acid, perchloric acid, andcombinations thereof. In certain embodiments, the leaching agent is abase, or a combination of several bases. Suitable bases include, but arenot limited to, a carbonate (e.g., at least one of sodium bicarbonate,ammonium carbonate, and dissolved carbon dioxide), a hydroxide base(e.g., at least one of sodium hydroxide, potassium hydroxide, andammonium hydroxide), gaseous ammonia, and combinations thereof. Incertain embodiments, the leaching agent is a salt. Suitable saltsinclude, but are not limited to, a cyanide (e.g., at least one of sodiumcyanide, potassium cyanide, and calcium cyanide), ferric sulfate, ferricchloride, cupric chloride, ferrous chloride, and combinations thereof.In certain embodiments, the leaching agent is ozone. In certainembodiments, the leaching agent is a thiosulfate (e.g., sodiumthiosulfate), thiourea, thiosulfuric acid, and combinations thereof. Incertain embodiments, the leaching agent is at least one of adithiooxamide (e.g., rubeanic acid) and a substituted dithiooxamide. Incertain embodiments, the leaching agent is a halogen-containingcompound. In a preferred embodiment, the leaching agent is selected fromthe group consisting of: an acid, a cyanide, and combinations thereof.

Suitable additives that may be utilized in the leaching compositioninclude, but are not limited to, an oxidant and a chelating agent.

A chelating agent may be utilized to sequester a desired metal for metalrecovery. In certain embodiments, a chelating agent is added tosequester a metal material that may interfere with leaching and recoveryof one or more desired metals. For example, a chelating agent may beadded to sequester calcium, magnesium, or other alkaline earth metalions in an aqueous phase of a metal-bearing slurry. The addition of achelating agent has been found to improve, for example, gold recovery insome ores. It is believed that chelating agents may controlprecipitation of insoluble salts and retard blocking of pores present inore particles by the insoluble salts. Sequestering the alkaline earthmetal ions is believed to promote good contact between the leachingagent and the desired metal (e.g., gold) of the ore particles. Forexample, the use of ethylene diamine tetraacetic acid, or salts thereof(either or both referred to herein as “EDTA”) as a chelating agent hasbeen found to improve gold recovery in some ores by about 5% to about10% compared to ore slurries without a chelating agent. Examples ofchelating or sequestering agents which may be used include, but are notlimited to, ethylenediaminetetraacetic acid, nitrilotriacetic acid,diethylenetriaminepentacetic acid, methanediphosphonic acid,dimethylaminomethane-1,1 diphosphonic acid,aminotrimethylenetriphosphonic acid, sodium hexamethaphosphate,1-hydroxyethane-1,1 diphosphonic acid, and salts thereof. The amount ofchelating agent added may vary depending on, for example, compositionalmakeup of the metal-bearing material. A chelating agent may be added inan amount of from about 0.04 to about 2 pounds of chelating agent perton of metal-bearing material (e.g., ore), or from about 0.8 to about1.4 pounds of chelating agent per ton of metal-bearing material.

Suitable solvents for inclusion in the leaching composition include, butare not limited to, water. Any suitable source of water for the aqueousleaching compositions may be used. For example, the water may be derivedfrom fresh water, sea water, brine, mixtures of water and non-toxicwater soluble organic compounds, recycled process water, or anycombination thereof.

In certain embodiments, the leaching composition may be an aqueoussolution comprising at least one leaching agent, and optionally one ormore additives. In certain embodiments, the leaching composition may bean aqueous solution including cyanide (e.g., from NaCN, KCN, and/orCa(CN)₂). In certain embodiments, the leaching composition may be anaqueous solution including thiosulfate (e.g., from sodium thiosulfate).In certain embodiments, the leaching composition is an aqueoushalogen-containing solution. The aqueous halogen-containing solution mayinclude one or more oxidizing agents. Suitable oxidizing agents includethose having a standard oxidation-reduction potential of over +900 mV,such as nitric acid, hydrogen peroxide, and chlorine. Such leachingcompositions may be suitable for recovering of gold from ore materials.

The leaching compositions may be applied to the metal-bearing materialin an amount sufficient to leach at least a portion of the metalcontained in the metal-bearing material, depending on several factorsincluding, but not limited to, the amount of metal-bearing material, thesurface area of the metal-bearing material, the concentration of metalin the metal-bearing material, the concentration of leachingcomposition, the equipment available to perform the leaching, and soforth. A person of skill in the art is able to determine the sufficientamount of leaching composition without undue experimentation.

Exemplary leaching agents/compositions are provided in Table 1.

TABLE 1 Leaching Agents/Compositions Category Leaching Agent ApplicationAcids Diluted H₂SO₄ Copper oxides, zinc oxide, lateritic nickel DilutedH₂SO₄ with oxidant Cu-, Ni-, and Zn-sulfides, oxidized uranium oreConcentrated H₂SO₄ Sulfided copper concentrate, laterites Nitric AcidCu-, Ni-, and Mo-sulfides, uranium concentrates, zirconium oxideHydrofluoric acid Columbite-tantalite ore Hydrochloric acid Titaniumores, nickel matte, reduced cassiterite Bases Sodium hydroxide BauxiteSodium carbonate Uranium oxide, scheelite Ammonium hydroxide Nickel,sulfide, copper sulfide, reduced laterite Salts Ferric sulfate/chlorideConcentrates of base metal sulfides Cupric chloride Concentrates of basemetal sulfides Cyanide salt (e.g., sodium cyanide, Gold and silver orespotassium cyanide, and/or calcium cyanide) Ferrous chloride Nickelsulfide Water Water Sulfides and chlorides, sodium vanadate, sodiummolybdate, sodium tungstanate

In a preferred embodiment, gold and/or silver is leached from ore thatcontains gold and/or silver using a cyanide salt. The cyanide salt isdissolved in an aqueous alkaline or neutral solution, which may beutilized as the leaching agent.

The disclosed methods may be used with any type of metal-bearingmaterial, such as an ore material, a concentrate, a precipitate, or anyother metal-bearing material from which a metal value may be recovered.The metal-bearing material may be an oxide ore, a sulfide ore, or acombination of oxide and sulfide ores. The minerals in the ore materialmay include a range of oxides, hydroxides, and sulfides. Metals that maybe extracted from the metal-bearing materials include, but are notlimited to, gold, silver, platinum, rhodium, iridium, osmium, palladium,aluminum, indium, gallium, tellurium, mercury, bismuth, cadmium, lead,zinc, copper, nickel, cobalt, molybdenum, rhenium, ruthenium, germanium,beryllium, iron, uranium, yttrium, titanium, lanthanum, cerium,praseodymium, neodymium, promethium, samarium, europium, gadolinium,terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, andcombinations thereof. In a preferred embodiment, the metals that arebeing extracted from the metal-bearing materials comprise at least oneof gold, silver and copper.

The disclosed methods may be used with any type of extractivemetallurgy. Extractive metallurgy includes the process of extractingmetals from metal-bearing materials (e.g., mineral ores) by physicaland/or chemical methods. Extractive metallurgy includes hydrometallurgy,pyrometallurgy, and electrometallurgy. Hydrometallurgy is the techniqueof extracting metals by aqueous physicochemical processes;pyrometallurgy involves dry physicochemical processes at elevatedtemperatures; and electrometallurgy deals with electrolytic methods.Electrometallurgy may be integrated with the other two processes, withelectrolysis in aqueous media being used in hydrometallurgy, andelectrolysis in smelted media being used in pyrometallurgy.

Extractive metallurgy processes may include operations to affect metalconcentration and/or separation. For example, extractive metallurgy mayinclude comminution methods (e.g., crushing or milling), physicalconcentration methods (e.g., magnetic, gravity, and electrostaticseparation), physicochemical concentration methods (e.g., flotation),and solid-liquid separation methods (e.g., filtration systems,counter-current decantation (CCD) circuits, thickeners, centrifuges, andthe like).

Hydrometallurgy is generally carried out in three distinct, sequentialphysicochemical stages: (a) selective dissolution of metals contained inthe solid phase (e.g., leaching); (b) purification and/or concentrationof the aqueous solutions containing the target metals (e.g.,precipitation, cementation, ionic exchange, or solvent extraction); and(c) selective recovery of metals (e.g., electrowinning, electrorefining,or hydrogen reduction).

Leaching of metal-bearing materials can be accomplished by affectingcontact between a metal-bearing material and a leaching composition. Thepregnant solution resulting from the leaching process can containdissolved metals (for example, indium, silver, gold, copper, zinc, lead,gallium, the like, or a combination thereof), residual leaching agents,and/or other materials. The soluble ions or metallic complexes in thepregnant solution can be selectively extracted from the pregnantleaching solution in downstream purification/extraction stages. Suchpurification/extraction stages may include, for example, solventextraction, filtering, centrifuging, electrolysis, electrowinning,precipitation, ion exchange, and/or flotation.

Leaching conditions may depend on the metal-bearing material to beleached and the selected leaching composition. Leaching can take placeunder ambient conditions, or at elevated temperatures and/or underelevated pressure. For example, the temperature may range from ambient(e.g., 10° C.) to 200° C.; the pressure may range from atmosphericpressure (e.g., 14.7 psi) to 750 psi. The time for extraction may varyfrom days to months to years depending on the particle size, mineralogy,rate of extraction, economics of continuing leaching, or a combinationthereof. Leaching may include different leaching cycles (e.g., batch,continuous, or intermittent multiple-batch); direction of flows (e.g.,co-current, counter-current, or hybrid); stages (e.g., single-stage,multiple-stage, or differential-stage); and contact methods (e.g.,percolation or dispersed solids).

The actual mechanism of leaching may involve simple dissolution madepossible by administration of a suitable solvent, or may involvedissolution made possible by a chemical reaction. The efficiency andrate of leaching may depend upon many factors, including the rate atwhich the leach solution is administered, the amount of metal in themetal-bearing material, and the conduciveness of the metal-bearingmaterial to leaching.

Leaching processes that may be used for recovery of metal values frommetal-bearing materials generally include in-situ leaching, dumpleaching, heap leaching, vat leaching, agitated leaching, or acombination thereof. Selection of the type of leaching process to beemployed may be based on several factors, such as for example, the gradeof an ore material, the clay content of an ore material, the hardness ofan ore material, or the way an ore material responds to various leachingmethods. A dump or heap leach system may provide reduced capital(equipment) costs and operating (energy) expense, and therefore may beselected for use with lower grade ore materials, or with higher gradeore materials that respond well to heap leaching, permitting a highmetal recovery. Agitation leaching, on the other hand, may provide for afaster and more complete recovery of a desired metal(s), may be easierto control, and may give higher recovery of secondary valuable metals,such as cobalt. Agitated leaching may require the capital cost ofadditional equipment, such as mills, leach tanks and clarifiers, and mayhave a higher operating cost because of, for example, the energyrequired to mill the metal-bearing material and the chemicals needed forsolids-liquid separation(s).

In-situ leaching includes applying a leaching solution directly on theplace where an ore is located within a mineral deposit itself. Thepregnant leach solution may then be pulled up and sent for subsequentpurification/extraction stages.

Dump leaching includes piling up a metal-bearing material and applying aleaching solution to the top of the dump from where it percolates bygravity, being collected at the bottom of the dump. Dump leaching may beused for run of mine (“ROM”) materials. Dump leaching may be preferredfor leaching of very low grades of target metal, usually below theeconomic cut-off grade for the main processing line, known asmineralized waste.

Heap leaching includes crushing a metal-bearing material, piling up thecrushed material, and applying a leaching solution to the top of theheap from where it percolates by gravity, being collected at the bottomof the heap. A heap may be at least 10 feet high, at least 30 or morefeet high, at least 100 feet or more in width, and up to about 2,600feet in length, on a commercial scale. The crushed metal-bearingmaterial may optionally be agglomerated (e.g., with concentratedsulfuric acid) prior to leaching to achieve a uniform particle size,which may improve uniform percolation of the leaching solution. In theheap leaching process, heaps can be either dynamic or permanent. In thecase of dynamic heaps, also called on-off heaps, the ore after beingleached may be moved to a location for final disposal of tailings andthe base of the heap may be re-used. In the case of permanent heaps, orstatic heaps, new heaps may be formed on top of previous ones, eitherusing or not the existing impermeabilized area.

Application and distribution of the leaching solution to a dump or heapmay be performed at the top of the dump or heap by, for example,drippers or wobbler-type sprinklers. The treatment fluids may percolateor seep through the heap. The typical application rate of a leachingcomposition is about 0.005 gallons of fluid per minute per square footof the heap's top surface. The percolation generally may be unassistedgravitational flow, and thus the flow rate may be determined primarilyby the application rate and the permeability of the heap. In general theflow rate of percolation through the heap can vary from about 0.001 toabout 0.01 gallons of fluid per minute per square foot (of a horizontalplane). When the fluids reach the impermeabilized area at the bottom ofthe dump or heap, they may drain or run off to the side to a pond orreservoir. The impermeabilized area may be formed of, for example,polyethylene or compacted clay. The pregnant solution containing thetarget metal and exiting the dump or heap may be sent for subsequentpurification/extraction stages for metal recovery. The leached ore maybe washed in order to recover retained leach solution containingdissolved metals and residual reagents such as acid.

Vat leaching (in static tanks) includes a set of usually squarecross-sectioned tanks, where a crushed metal-bearing material (e.g., acrushed ore) is loaded and a leaching solution is applied so as to floweither upwardly or downwardly, thereby inundating the layer of crushedmaterial. The flow of leaching solution may be laminar. The leachingcycle may be 6 to 12 days.

Agitated leaching includes dispersing an aqueous slurry of crushed andmilled metal-bearing materials in one or more stirred tanks. Thecombination of a liquid with the metal-bearing material to form a slurrycan be accomplished using any one or more of a variety of techniques andapparatus, such as, for example, in-line blending or using a mixing tankor other suitable vessel. The slurry may have a concentration of solidmetal-bearing material (the slurry density) on the order of less thanabout fifty (50) percent by weight of the stream, and preferably aboutforty (40) percent by weight of the stream. Other slurry densities thatare suitable for transport and subsequent processing may, however, beused. The slurry of metal-bearing material may be dispersed into theleaching solution by, for example, gas injection or mechanicalagitation.

Agitated leaching may be conducted at atmospheric pressure, increasedpressure, or a combination thereof. Crushed metal-bearing material thatis to be agitation-leached may be ground or wet-milled to a desired sizedistribution for achieving an acceptable metal recovery in leaching,with the resulting metal-bearing solids being added to the agitationleach unit(s) as an aqueous slurry. The material may be ground to100%—65 Tyler mesh, or 100% Tyler mesh. The solids content of the slurrymay be between 35% and 55%, or between 40% and 50% by weight. Theaqueous portion of the slurry may be derived from, for example, freshwater, sea water, brine, mixtures of water and non-toxic water solubleorganic compounds, recycled process water, or any combination thereof.Thus, in agitation leaching, a considerable amount of water may benormally brought into the leaching system with the metal-bearingmaterial. This water may eventually leave or be removed from the systemin order to maintain a water balance. Water may be removed from thesystem with the leached solids in the tailings, or by intermittentbleeds from the circuit. At the conclusion of agitated tank leaching,the leached solids can be separated and washed using, for example,counter-current thickening and washing, filtration, or a combinationthereof. Any desired metal or other valuable metals in the water leavingwith the leached solids may be lost (called the “soluble metal loss”).Leaching agent in this water may also lost and may be neutralized priorto the final disposal of the leached solids. In comparison with othermethods, leaching time in agitated leaching may be smaller due tosmaller particle size (greater specific area) and due to the turbulencein the tank, which provides higher diffusion between reagent andmetal-bearing material.

Hydrometallurgical extractive processes may be sensitive to particlesize. Some metal-bearing materials are quite permeable to leachcompositions; hence, relatively large particles of the material can beeffectively leached. Many metal-bearing materials are, however, ratherimpermeable. If the particles are too large, a leach composition may notpenetrate to the interior of the particles, and leaching may beincomplete. Further, use of large particles may result in a percolationrate too rapid for effective heap or dump leaching. Materials maytherefore be reduced in size before leaching in order to increase thesurface area of the material being treated and to decrease therequirement for the leach composition to penetrate deeply into theparticles. On the other hand, if the particles are too small, althoughthe metal-bearing material may be effectively penetrated by the leachsolution, the percolation rate may become so slow as to be impractical.Undersized particles may therefore be “agglomerated,” such as by theaddition of a cement.

The metal-bearing materials subjected to leaching may be reduced to aparticle size in the extraction processes as appropriate. Various broadparticle size ranges may be engineered in order to use heap or dumpleaching, vat leaching, agitated leaching, or a combination thereof. Forexample, heap or dump leaching may be performed using material crushedto a P80 (product size is 80% passing the nominal size listed) of about⅛ inch to greater than about 1 inch. Agitated leaching may be performedat a size of less than about 500 μm (about 0.5 mm). In variousembodiments, it may be desirable to have a finer size than about 500 μmto reduce any potential problems with abrasion. In various embodiments,agitated leaching may be performed at a size of about 50 In variousother embodiments, vat leaching may be performed using material crushed(and optionally ground for the finer size range) to a P80 of about 0.2inch (about 0.5 mm) to greater than about 1 inch.

A variety of acceptable techniques and devices for reducing particlesize of the metal-bearing material may be used. Suitable devicesinclude, but are not limited to, ball mills, tower mills, superfinegrinding mills, attrition mills, stirred mills, or any combinationthereof. Controlled fine grinding may be achieved using a fine grindingapparatus, such as, for example, a stirred horizontal shaft mill withbaffles or a vertically stirred mill without baffles. If a horizontalmill is utilized, any grinding medium that enables the desired particlesize distribution to be achieved may be used, the type and size of whichmay be dependent upon the application chosen, the product size desired,grinding apparatus manufacturer's specifications, and the like.Exemplary media include, for example, sand, silica, metal beads, ceramicbeads, and ceramic balls.

In various embodiments, crushing of metal-bearing materials may beconducted without water addition. However, in other embodiments,optionally “water-flush” crushing may be used to elutriate the finematerials formed during the crushing operation, or a combination of drycrushing and “water-flush” crushing. In various embodiments, grindingcan be conducted with water addition. Water addition for grinding may beobtained, for example, from available fresh water, brackish water,recycle neutral chloride-containing solutions or any other source.

Particles of metal-bearing material by undergo size classification.Cyclone technology (e.g., use of cyclones, or mini-cyclones) may beutilized to facilitate size classification of relatively coarsematerials from relatively fine materials. An optional solid-liquidseparation stage may be utilized to remove excess processing liquidwhere the chosen grinding method and apparatus utilize a liquidprocessing agent (such as, for example, process water) to facilitategrinding (e.g., in a super-fine grinding stage).

In certain embodiments, the metal-bearing materials may be agglomeratedto increase particle size for leaching. Crushed metal-bearing materialmay be sent to an agglomeration unit by, for example, a conveyor belt.If necessary, water may be added to the crushed product duringtransport, for example in cases in which a metal-bearing material isvery dry and contains a high amount of fines. Addition of water onto theconveyor belt may be performed in several ways, such as spraying, andmay minimize dust formation, thereby rendering more favorable workingconditions. The crushed material may then be sprayed with an aqueoussolution containing an agglomeration aid, and tumbled. The amount ofwater applied to the material during this spraying may generally be fromabout 2, or 3, percent to about 10 or 12 percent, based on the weight ofthe material (e.g., ore as mined contains about 3 to about 10 percentwater, the balance being solids that would remain upon oven drying). Anagglomeration aid may be dissolved in that water at a concentration toprovide an amount of agglomeration aid in the metal-bearing materialthat is effective to provide the permeability desired. During or shortlyafter the spraying of an agglomeration aid solution, mechanicalagitation of the materials may be required to distribute theagglomeration aid through the materials. Such mechanical agitation maybe provided by tumbling (e.g., tumbling with an aqueous solution ofagglomeration aid may be done in a rotary drum agglomerator or pug mill,or the metal-bearing material can be treated and tumbled by mechanicalaction of a conveyor belt transfer point, or the cascading of materialas a heap is formed). The tumbling action may be provided for a veryshort time period, and generally that time period is less than a minute.

An aqueous leach composition containing the leached metal (also referredto as a “pregnant solution”) can then be directed to further extractionand purification processes to recovery a selected metal value. Thepregnant solution from a leach process may undergopurification/extraction stages as appropriate to recover the desiredmetal value(s). Suitable processes include, but are not limited to,metal recovery through precipitation, cyclonic separation, thickeningand filtering, electrowinning, electrolysis, solvent extraction,activated carbon adsorption, ion exchange resin adsorption, recycling ofleaching solution, or any combination thereof. Activated carbon or ionexchange resins may be separated from a leach residue by screening, forexample.

Solvent extraction can be carried out in any known manner. Pregnantsolution may be contacted with an organic phase containing ametal-specific extraction reagent. The metal-specific extraction reagentmay extract the metal from the aqueous phase into the non-aqueous phase.Each extraction performed can be carried out by mixing an organic phaseand a pregnant solution and allowing the two phases to settle. Thismixing-settling can be carried out in multiple series of mixing-settlingtanks with countercurrent flow of the aqueous and non-aqueous phases.Solvent extractions may be carried out using mixer-settler solventextraction units, wherein the organic phase and the aqueous leachsolution are vigorously intermixed in a mixer, and the resultingdispersion of organic and aqueous is then passed to a settler where thetwo phases settle, and from which there exits a clear organic phase anda clear aqueous phase. A solvent extraction process may include, forexample, 2 extraction stages and 2 strip stages or 2 extraction stagesand 1 strip stage. Another example is 1 extraction stage followed by 2extraction stages and 1 strip stage in what is called the seriesparallel stage configuration. In the series parallel stagingconfiguration, the high grade leach solution may be treated in the 2extraction stages and the low grade leach solution in the singleextraction stage. In some cases wash stages may also be employed. Aftersolvent extraction, the pregnant solution, now depleted in metal, may berecycled back to a leaching process. The leach solution depleted inmetal that exits the solvent extraction process may be called araffinate. The solvent extraction process may recover some 80 to 95% ofthe metal in the leach solution. Thus, the raffinate may contain about5-20% of the leached metal. The raffinate may be recycled back to theleach process and provide the bulk of a leach solution used in aleaching process.

Efficiency of the metal recovery may be enhanced, at least in part, byminimizing the losses of soluble metal in the remaining solid materials(e.g., pulp materials), which constitutes the waste. The leached solidsfrom a leach process may be treated with chemical or physical processesor a combination of chemical or physical processes in order to renderthe materials acceptable for environmental disposal. The leachingprocess may also be applied to a concentrate that is recovered from theore using physical or chemical concentration methods or a combination ofchemical or physical methods.

The foregoing may be better understood by reference to the followingexample, which is presented for the purpose of illustration and is notintended to limit the scope of the invention.

Example

A gold containing ore was treated with 20 ppm and 40 ppm of a surfactantcomposition comprises 17.3% (i.e., about 17%) sodium dodecyl benzenesulfonate; 1.0% (i.e., about 1%) cold pressed orange peel oil; 0.6%(i.e., about 0.6%) of cocodiethanolamide; and 0.13% antioxidant; withthe balance being water (all percentages are by weight) and the amountof gold extracted was measured and compared to an untreated sample.Surfactant blend product was added to a gold containing ore treated withcyanide and evaluated using a standard bottle roll test. Bottle rolltests were conducted with varied doses from at 0 ppm, 20 ppm, and 40ppm. As shown in Table 2, the amount of gold extracted in the treatedsamples was higher when compared to the untreated samples. Although thetest was conducted using a particular surfactant composition, othersurfactants and/or polymers that reduce surface tension of the barrensolution are expected to enhance leaching efficiency in a similarmanner. The surfactants can be applied to metal-bearing materialscontaining, e.g., any high valuable metal such as, e.g., gold, silver,and copper.

TABLE 2 Gold Extraction Calculated on Solids Surfactant Dosage AverageLeaching Efficiency  0 ppm 83.76% 20 ppm 84.26% 40 ppm 84.77%

Any ranges given either in absolute terms or in approximate terms areintended to encompass both, and any definitions used herein are intendedto be clarifying and not limiting. Notwithstanding that the numericalranges and parameters setting forth the broad scope of the invention areapproximations, the numerical values set forth in the specific examplesare reported as precisely as possible. Any numerical value, however,inherently contains certain errors necessarily resulting from thestandard deviation found in their respective testing measurements.Moreover, all ranges disclosed herein are to be understood to encompassany and all subranges (including all fractional and whole values)subsumed therein.

All references, including publications, patent applications, andpatents, cited herein are hereby incorporated by reference to the sameextent as if each reference were individually and specifically indicatedto be incorporated by reference and were set forth in its entiretyherein.

Preferred embodiments of this invention are described herein, includingthe best mode known to the inventors for carrying out the invention.Variations of those preferred embodiments may become apparent to thoseof ordinary skill in the art upon reading the foregoing description. Theinventors expect skilled artisans to employ such variations asappropriate, and the inventors intend for the invention to be practicedotherwise than as specifically described herein. Accordingly, thisinvention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw. Moreover, any combination of the above-described elements in allpossible variations thereof is encompassed by the invention unlessotherwise indicated herein or otherwise clearly contradicted by context.

What is claimed is:
 1. A method of extracting metal from a metal-bearing material, the method comprising: forming a slurry comprising the metal-bearing material, water, a surfactant composition, and a leaching composition; and recovering at least a portion of the metal from the slurry.
 2. The method of claim 1, wherein the metal-bearing material is comminuted prior to formation of the slurry.
 3. The method of claim 1, wherein the surfactant composition comprises an anionic surfactant selected from the group consisting of: an alkyl aryl sulfonate, an olefin sulfonate, a paraffin sulfonate, an alcohol sulfate, an alcohol ether sulfate, an alkyl carboxylate, an alkyl ether carboxylate, an ethoxylated alkyl phosphate ester, a monoalkyl sulfosuccinate, a dialkyl sulfosuccinate, a monoalkyl sulfosuccinamate, a dialkyl sulfosuccinamate, and combinations thereof.
 4. The method of claim 1, wherein the surfactant composition comprises a cationic surfactant selected from the group consisting of: an alkyl trimethyl quaternary ammonium salt, an alkyl dimethyl benzyl quaternary ammonium salt, a dialkyl dimethyl quaternary ammonium salt, an imidazolinium salt, and combinations thereof.
 5. The method of claim 1, wherein the surfactant composition comprises a nonionic surfactant selected from the group consisting of: an alcohol alkoxylate, an alkylphenol alkoxylate, a block copolymer of ethylene oxide, a block copolymer of propylene oxide, a block copolymer of butylene oxide, an alkyl dimethyl amine oxide, an alkyl-bis(2-hydroxyethyl) amine oxide, an alkyl amidopropyl dimethyl amine oxide, an alkylamidopropyl-bis(2-hydroxyethyl) amine oxide, an alkyl polyglucoside, a polyalkoxylated glyceride, a sorbitan ester, a polyalkoxylated sorbitan ester, an alkoyl polyethylene glycol ester, an alkoyl polyethylene glycol diester, and combinations thereof.
 6. The method of claim 1, wherein the surfactant composition comprises a high terpene-containing natural oil.
 7. The method of claim 6, wherein the high terpene-containing natural oil is selected from the group consisting of: orange peel oil, grapefruit peel oil, lemon peel oil, pine oil, and combinations thereof.
 8. The method of claim 1, wherein the surfactant composition is present in the slurry at a concentration of from about 1 gram of surfactant composition to about 10,000 grams of surfactant composition per metric ton of metal-bearing material.
 9. The method of claim 1, wherein the surfactant composition is present in the slurry at a concentration of from about 10 grams of surfactant composition to about 100 grams of surfactant composition per metric ton of metal-bearing material.
 10. The method of claim 1, wherein the leaching composition comprises a leaching agent selected from the group consisting of: nitric acid, hydrofluoric acid, hydrochloric acid, sulfuric acid, phosphoric acid, perchloric acid, a carbonate, a hydroxide base, gaseous ammonia, a cyanide salt, ferric sulfate, ferric chloride, cupric chloride, ferrous chloride, ozone, a thiosulfate salt, thiourea, thiosulfuric acid, dithiooxamide, a substituted dithiooxamide, a halogen-containing compound, and combinations thereof.
 11. The method of claim 1, wherein the leaching agent is at least one of sodium cyanide, potassium cyanide, and calcium cyanide.
 12. The method of claim 1, wherein the recovered metal is at least one of gold, silver, and copper.
 13. The method of claim 1, wherein the metal-bearing material is ore.
 14. A method of improving leaching efficiency in a metal extraction process, the method comprising: treating a metal-bearing material with a surfactant composition; and subjecting the treated metal-bearing material to a metal extraction process.
 15. The method of claim 14, wherein the metal-bearing material is communited before or during treatment with the surfactant composition.
 16. A slurry comprising: water; a metal-bearing material comprising at least one of gold, silver, and copper; a high terpene-containing natural oil; and a leaching agent comprising at least one of an acid and a cyanide.
 17. The slurry of claim 16, wherein the high terpene-containing natural oil is selected from the group consisting of: orange peel oil, grapefruit peel oil, lemon peel oil, pine oil, and combinations thereof.
 18. The slurry of claim 16, wherein the high terpene-containing natural oil is orange peel oil.
 19. The slurry of claim 16, wherein the metal-bearing material comprises gold.
 20. The slurry of claim 16, wherein the leaching agent comprises a cyanide. 